Radio receiving system



Feb. 3, 1931.

L. L. JONES 1,791,030

RADIO RECEIVING SYSTEM Filed March 6, 1928 A B C RF: H GH G \N S AGE AUDO LOUD AMPUFIER DETECTOR I AMPLIFIER S EAKER r 13.2. D A B s c 1 DETECTOR o g I f g REHIGH GAIN g p f AMPLIFIER j III PC ER (-ZOV.) A nYE C C A B +200v.

unscrew 26 1511c FOR BIASED DETECTOR VOLTAGE 9o VOLTS DETECTOR CHARACTERISTIC FOR 2 GRID LEAK AND CONDENSER o 1 z 3 4 5 e 7 a 9 :0

DETECTOR INPUT VOLTAGE (Rf) INVENTOR Les1"er L.Iortes A v NEYS Patented Feb. 3, 1931 the detector tube to 'satu OFFICE LESTER L. JONES, OF ORADELIi, NEW JERSEY RADIO RECEIVING SYSTEM v Application filed March 6,

This invention relates to radio receiving systems and has special reference to the provision of an electron discharge tube radio receiving circuit or system of high power embodying only a single stage of audio amplification.

As iswell known, a common type of radio receiving system comprises a multi-stage radio frequency amplifier, a detector anda multi-stage audio frequency amplifier, all arranged in cascade. In this type of radio re-' ceivingsystem the multi-st-age radio frequency amplifier is built so as to develop just sufficient radio frequency voltage for the input of rate a detector tube operating with a grid condenser and a grid leak; and the audio frequency amplifier is built to am produced by the detector to a degree sufii'cient to operate the translating instrument, such as a loud speaker. In order to obtain a sufficient amount of amplificationof the audio output of-the detector, it has generally been necessary to use two or more stages of audio frequency amplification.

The use of a number of stages of audio frequency amplification in the audio amplifiers of prior radio receiving systems was necessitated bythe low audio power delivered by the detector tube but such multi-stage audio frequency amplifiers are attended with a number of serious disadvantages. 'The plurality of audio stages is accompanied by distortional effects which are the geometric product of the distortions due to the several tubes of the audio amplifier and the last tube or stage of the amplifier is subject tothe liabilityof becoming overloaded in the operation of the system, resulting in the depre-, ciati'on of the tone quality ofthe receiving system. Thenecessity of thus using two or more stages of audio amplification, as compared with the use of a single stage of audio amplification results in an increase, not only in the cost of the, receiving system, but also in the cost of equipment which isprovided inpower operated receivers for filtering out the supply voltage fluctuation, it belng necessary to filter out such fluctuations to a high degree in receivers using high audio-.ampli- 4 audio output.

plify the rectified or audio voltage 1928. Serial No. 259,451.

fication. These disadvantages disappear when a single stage of audio amplification is used, but in systemsof the prior art the volume produced by a single stage of audio amplification isinsufiicient for loud speaker operation,-tl1is' being due to the saturation effect in the. detector which prevents it from developing more t The prime object of my present invention is directed to the provision of a radio receiving system embodying only one stage of audio amplification, with all the advantages consequent thereto, in which the detector is capable of developing an audio "output ofa magnitude suflicient to be amplified by said single-stage of audio amplification for full loud speaker operation.

I have discovered that the detector tube or stage may be given such predetermined constants,,and that the-radio frequency amplifier may be related to the-detector in such a Way, as to generate suflicientaudio output in the detector to fully load a single stage of amplification such as that provided by a power tube, and thus produce suflicient audio amplification for all normal loud speaker operations. I have further empirically determined that the constants of the audio frequency stage may be so related to those of the detector and radio amplifier stages that an a small amount of the audio tube may be fully loaded by the I audio output developed by the detector without causing any overloading of said audio tube over any part of the range of detection operation of said detectorstage. The prime object of my present invention centers about the production of radio receiving apparatus in which these discoveries are applied.

'To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consistsin the'method and the circuit elements and their relation the other, as hereinafter are more particu larly described and sought to be defined in the claims, reference being bad to the accompanying drawings which show the. preferred embodiment of my invention, and in which: 1

Fig. -l is a schematic view showing the inone to terrelation of the parts of a radio receiving system embodying the invention,

Fig. 2 is a wiring diagrammatic view of the same showing the circuit interrelation be tween the parts or sections thereof, and

Fig. 3 is a view of a graph explanatory of some of the principles of the invention.

Referring now more in ings and havingreference first to Figs. 1 and 2 thereof, my invention comprises the arrangement in cascade or series of a radio frequency amplifierv generally designated as A embodying a plurality of radio frequency stages, a detector stage B of the vacuum tube type, a single step or stage audio amplifier C embodying a power tube, and an audio translating apparatus such as the loud speaker D of any approved type, the constants of the detector B being so predetermined and the constants of the radio frequency amplifier A and audio frequency amplifier C being so related thereto that the detector 1s capable of developing a high audio output which may be sufiiciently amplified by the single audio stage C to produce full volume operation of the loud speaker D. I have empirically determined that when the detector tube B is operated by grid bias rather than by a leaky grid condenser, an is furthermore provided with a high biasing grid voltage and with a correspondingly high plate voltage, and that when the detector tube is supplied with a sufiiciently high radio frequency input comparable in voltage to the high grid biasing voltage, the detector tube is capable of developing an audio output'of a magnitude sufficient to permit its working directly into, and fully loading a power tube audio stage. More specifically I have found that when the bias on the grid of the detector stage is raised to the order of 10 to 20 volts, with a correspondingly high plate voltage such as 100 to 200 volts, and when the radio frequency amplifier is built to produce a high gain or amplification enough to develop a high radio frequency voltage at the input of the detector, over a range of 1 to 10 volts, the desired high audio output is produced capable of employment with a single power stage related thereto so as to be fully loaded thereby.

In applying these discoveries, Ifirst deter- .mine the constants to be imposed upon the detector tube B, which detector tube may comprise a three-element electron discharge device having a filament or cathode f fed by a filament supply A, an input or grid-filament circuit z' connected to the output of the R. F. amplifier A and an output circuit 0 connected to the plate p of the tube, the said output circuit including a primary P of an audio transformer 'T having the secondary S. These imposed constants include the biasing of the grid g of the detector tube negatively with a voltage of the order of at least 10 to detail to the drawficient to swing the grid be minus 20 volts, while the applied platevoltage is about 200 volts. Then in order to utilize for the purposes of my invention the long straight line portion of the detection characteristic of a detector having these imposed constants, the input voltage at the input circuit 11 of the detector is made high enough to produce a grid swing of the order of magnitude of the biasing grid. voltage, namely, of the order of 10 to 20-volts. This I accomplish by the use of a high gain radio frequency amplifier A which may, ample, comprise quency amplification of the untune d type organized and arranged as disclosed and claimed in my copending application, Serial No. 205,934 for radio receiving apparatus, filed July 15, 1927; By -means of these, constants I am enabled first, to produce a long linear detection characteristic for the detector, as shown in Fig. 3 of the drawings, and

' then to provide a radio frequency input voltage for the detector of a magnitude sufover a voltage sufficient to utilize substantially the full linear portion of said detection characteristic. The detector stage B is thereby enabled to yield an audio output of sufficient power to workdirectly into the single stage power tube C.

v The constants of the single power stage C are then determined so that output of the detector is amplified to produce the same being supplied by a bat-.

; and as shown 1n Fig.

the high .audio for exfive stages of radio frefull volume operation of the loud speaker D,

and preferably so that at the saturation point of the detector stage B the power tube C is just fully loaded, this ity of overloading the power tube. To accomplish these results, the power stage which also comprises a three element electron discharge device having the filament or cathode f, the grid energized at a fairly high voltage, usually of the order of 50 volts, in order to deliver the fulloutput'. In order to generate a commensurate audio frequency voltage on the grid of the power tube, the ratio of the transformer T should be a step-up ratio, of approximately 3 to 1, the audio output tor tube B having the aforesaid constants supplying approximately 20 volts With known power tubes having an amplification factor of 3, the 50 volts developed on the and therefore to a swing of over 400 volts.

which is approximately as high day power equipment provides. Therefore, to interrelate the single stage audio amplifier with the preceding parts of the system, I first determine the maximum audio output voltage as present obviating the possibil-v of the detecof the detector and then the maximum load 1 and provide a. step-up transformer between the detector and audio tube 'so that its ratio is the ratio of these two voltages. If the trans- -former ratio is higher than can be commercially achieved is also preferably without introducing frequency distortion, then the biasing voltages on the detector. should-be correspondingly increased. The grid g of the power tube .0

biased of a voltage supply C which may deliver. say, a minus 40'volt bias,

and the plate 11' of the tube may be provided with voltages ofabout 200 volts from the battery or other supply B. Y 1

In Fig. 3 of the drawings I'show graphically a curve representing the detector characteristic produced by biasingthe 4 grid in accordance with the rinciples of my'present 2o invention, the sa-mebeing compared with the teristics with respect .age'sare plotted as abscissa:

value of the curves a:

detector characteristic of a prior art, using 'a grid leak and condenser. In this graph, the R. F. detector input volt and the audio detector output voltages are plotted as or.- dinates, the dotted curve in representing the detection characteristic when the grid is biased negatively with 9 volts, and: when 'a' plate voltage of 90 volts is used. The full line curve 3 is fora grid leak and'condenser type' ofdetector with the conventional .00025 grid condenser an'd"2 megohms grid mmfd.

leak, using 45 volts for the plate. By comparison of these two curves it will be seen that the'saturation curve of the detector characteristic 2 is reached when the audio output voltage is below 4 volts, while the-saturation of the detection characteristic 00 resulting from the employment of the principles of my lnvention is at or about an audio output' voltage of 30 volts. These voltages are stepped-up approximately 3 to lby the audio transformer T. The relative linearity of the two characteristics'm and 3 can be determined by reference to the straight lines J and K.

drawn from the origin othrough a mean lines representing theidea-l detector characoutput voltage to input Voltage. Referring to the biased grid curve as in the region of 27 volts, it will be seen that the characteristic is 13% over the ideal condition, while at 2.7 volts 5 the value) it is about 54% of the ideal condition. the grid leak characteristic are 15% over and only 38% at the voltage value. If the comparison be made on the basis of similar fractional parts of the input voltage the grid leak characteristic is about only 10% of the ideal curve at the lower value. This comparison illustrates the greater proportionality of the high grid bias curve 00 when used over its whole length.

The various advantages resulting from the negatively -by'means detector of the.

the systems of and 3 these straight remains constant over a to proportionality of Corresponding values for supplies a radio frequency' input for the detector having a'volt--' I age comparable in magnitude with thehigh grid biasing voltage of the detector, the magnitude'being sufficient to swing the grid over a voltage utilizing in the audio output of the detector the full linear portion of the detector characteristic a: thereof. The constants of the system aresuch that the detector approaches saturation just before the power tube is fully loaded, and when the detector' saturates and is incapable of giving forth more audio signal the power tube is just fully loaded and therefore cannot be overloaded upon saturation of the detector. A improved tone quality is therefore made possible because of the operation of, the detector overja greater portion of its linear characteristic. The receiving set may be made more economically because of-the lower cost of the additional radio frequency amplification required by the high gain R. F. amplifier as compared with the: cost of additional audio frequency amplification. This cost can be reduced further'especially in power operated receivers because of the possible elimination of equipment for filtering out supply voltage fluctuations to the high degree that was previously found necessarywith receivers using high audio amplification.

greatly Another important advantage of the sys tem of my invention which further shows the characteristics thereof as'comparedwith the prior art is the substantial freedom of my-system from fading-effects.

lVhere the detector voltages are set at values just high enough to fully load the audio tube as the detector saturates, a large increase of radio frequency causes no increasein audio volume and produces extremely slight changes in the tone quality of the audio output. I Then when the signal increases in intensity due to transmission effects, the loud speaker volume does not change. Similarly, when the transmission is weakened, the loud speaker volume considerable degree of weakeningof the signal, because the weakening of the signal merely produces aless'er amount of saturation of the detector. This phenomena produces the-equivalent of automatic volume controls which are coming. more'into use at the present time. In the prior art systems, however, on the contrary, the detector was workedat a region well below saturation.

input into the detector Although the voltage outi putof the detector was small, it was followed by a sufficient amount of audio amplification to enable this small'output to fully load the power tube; then when'the signal intensity as to be subject to the disadvantages flowing from fading effects.

While I have shown and described my invention in the preferred form, it will be apparent that may be made in the structure out departing from the spirit of the invention, defined in the following claims.

I claim:

1. An electron discharge tube radio receiving circuit comprising a multi-tube radio frequency amplifier, a grid biased tube detector, a single stage audio frequency amplifier, and a loud speaker all arranged in cascade, means to impress a high biasing voltage on the grid of the detector tube, a source of high plate voltage therefor, the grid and plate voltages being sufficiently high to give the detector characteristic a large that if substantially fully utilized the detector output need only be amplified by the single stage audio frequency amplifier to produce full volume operation of said loud speaker, and the gain in the multi-sta-ge radio frequency amplifier being high enough to provide an input for the detector tu e of suificient magnitude to utilize substantially the full linear portion of the detector characteristic thereof.

2. An electron discharge tube radio receiving circuit comprising a multi-stage radio frequency amplifier, a tube detector, a single stage audio frequency amplifier,- and a loud speaker all arranged in cascade, means to impress a biasing voltage on the grid of the detector tube of the order of at least 10 to 20 volts, the gain in the radio frequency amby the single stage audio plifier being suflicient to supply an input voltage to the detector comparable in magnitude with the high grid biasing voltage thereof, and a source of commensurately high plate voltage for the detector, whereby the resulting augmented audio frequency output developed by the detector tube is sufficiently amplified by the single stage audio frequency amplifier to produce full volume operation of said loud speaker. l

3. An electron discharge tube radio receiving circuit comprising a multi-stage radio frequency amplifier, a tube detector, a single stage audio frequency amplifier, and a loud speaker all arranged in cascade, the circuit constants including a high biasing voltage for the grid of the detector tube, a high gain for the radio frequency amplifier suificient to supply an input voltage to the detector comparable in magnitude with the high grid biasing voltage thereof, and a high plate voltage for the detector, whereby the resulting augmented audio frequency output developed by the detector is sufficiently amplified frequency amplifier to produce full volume operation of said loud speaker, and the single stage audio frequency amplifier having constants so related to the many changes and modifications disclosed withlinear portion so constants that at said preceding circuit by the detector is audio output developed sufficient to substantially fully load the audio fre uency amplifier but insufiicient to overloa thesama- 4. An electron ceiving' circuit comprising a 'multi-stage radio frequency am lifier, a tube detector, 9. single stage audio requency amplifier, and a loud speaker, means to impress a biasing voltage on the grid of the detector tube of the order of at least 10 to 20 volts, a source of commensurately high plate voltage therefor, the radio frequency amplifier having a gain sufliciently high to provide a radio frequency input for the detector tube of a magnitude sufiicient to utilize substantially the full linear portion of the detection characteristic thereof, the single stage audio frequency amplifier comprising a power tube connected by a step-up transformer to the output circuit of the detector tube and so related to said preceding circuits as to permit the power tube to be substantially fully loaded by the audio frequency output of the detector, and further so related to the linear portion of the detection characteristic as to prevent over-loading of said power tube when the entire linear portion of said detection characteristic is utilized.

5. In the operation of a radio receiver including radio. and audio frequency amplifiers, a loud speaker, and a detector, the method of avoiding difficulties caused by multistage audio frequency amplification and of obstaining the desired loud speaker output volume which includes decreasing the audio frequency amplification to a gain conveniently obtainable in a. single stage thereof, commensurately increasing the radio frequency amplification to obtain the desired undiminished audio frequency output volume, and sufficiently raising the saturation point of the detector to accommodate-the increased ener%y supplied thereto.

6. n the operation of a radio receiver including radio and audio frequency amplifiers, a detector tube, and a loud speaker, the method which includes decreasing the audio fre uency amplification to a gain convenient- 1y 0 tainable in a single stage thereof, commensurately increasing the radio frequency amplification to obtain the desired loud speaker volume, obtaining rectification in the detector tube by biasing the grid thereof, and increasing the grid bias and anode potentials applied thereto in order to sufficiently raise the saturation point thereof to accommodate the increased radio frequency energy without distortion.

7. In the operation of a radio receiver indischarge tube radio re-- and of obtaining the desired loud speaker output volume which includes audio frequency amplification to a gain conveniently obtainable in a slngle stage thereof, commensurately increasing the radio frequency amplification to obtain the desired.

undiminished audio frequency output volume, and raising the saturation point of the detector sufiiciently to accommodate the increased energy supplied thereto but insufficiently to overload the audio frequency amanode potentials applied thereto in order to f to accommodate the increased radio 8. In the operation of a radio receiver including radio and audio frequency amplifiers, a detector tube, and a loud speaker, the method which includes decreasing the audio frequency amplification to a gain conveniently obtainable in a single stage thereof, commensurately increasing the radio frequency amplification to obtain the desired loud speaker volume, obtaining rectification in the detector tube by biasing the grid thereof, and increasing the grid bias and raise the saturation point thereof sufliciently .freenergy without distortion, but insufiito overload the audio frequency a1nquency ciently plifier.

9. In the operation of a radio broadcast receiver having a detector and an audio frequency amplifier including a power tube, the

' method of preventing the undesirable distortion caused by overloading of said power tube which includes so adjusting the con stants of the detector that it will saturate at a value at or below that which is capable of overloading said-power tube- 10. A radio receiver comprising a radio frequency amplifier, a detector, an audio frequency amplifier, and a translating device necessitating an audio frequency output volume ordinarily obtained by the use of two or more audio frequency amplifying stages, the audio frequency amplifier consisting of only a single stage, the radio frequency amplifier having a, commensurately increased gain in order to obtain the desired audio frequency output volume without dimlnution, and the detector having a sufliciently high saturation point to accommodate the Y tube being operated by biasing the grid thereof, a source of a relatively high grid bias potential therefor, a source of relatively high anode potential therefor, the grid decreasing the high to raise the saturation point of the detector sufficiently to accommodate the increased. radio requency energy supplied thereto without distortion.

12. A radio receiver comprising a radio frequency amplifier, a detector, an audio frequency amplifier, and a translating device necessitating an audio frequency output volume ordinarily obtained by the-use of two or more audio frequency amplifying stages, the audio frequency amplifier consisting of only a single stage, the radio frequency amplifier having a commensurately increased gain in order to obtain the desired audio frequency output volume Without diminution, and the detector sufliciently high to accommodate the increased radio frequency energy, but insufli ciently high to permit overloading of the audio frequency amplifier. I

13. A radio receiver comprising a radio frequency amplifier, a detector tube, an audio requency amplifier, and a loud speaker, the audio frequency amplifier consisting of only a single stage, the gain in the radio frequency amplifier being commensurately increased in order to obtain the desired loud speaker volume, and the detector tube being operated by biasing the grid thereof, a source of a relatively high grid bias potential therefor, a source of relatively high anode potential therefor, the grid bias and anode potentials being sufiiciently high to raise the saturation point of the detector suifici'ently to accommodate the increased radio frequency energy supplied thereto without disa detector and an audio frequency amplifier including a power tube coupled thereto, the constants of the detector being so adjusted as to saturate at an energy value at or below that which is capableof overloading the power tube, in order to prevent overloading anld undesirable distortion ,in' said power tu e.

Signed at New York, in the county of New ork and State of New York, this 3rd day of March, A. D. 1928.

LESTER L. JONES.

having a saturation point DISCLAIMER 1,791,030.Lester L. Jones, Oradell, N. J. RADIO Rmcmvma SYs'mM. Patent dated February 3, 1931. Disclaimer filed April 29, 1936, by the assignee, Radio Corporation of America. Hereby enters this disclaimer to that part of the specification which consists of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14.

- [Qfici 0026116 May 19, 1936.] 

